In 1989, the 50 state geological surveys were polled to see how much of their territory had been mapped to the scale of a 7.5-minute quadrangle. The results were disturbing.

Only 19.6 percent of the land in the United States had been mapped at that level of geologic detail. And in many cases, important environmental and economic decisions were being made on the basis of geologic mapping that was nearly a century old.

A national need was clearly not being met. The Association of American State Geologists (AASG) and the U.S. Geological Survey (USGS) began efforts to develop federal legislation that would advance and support geologic mapping in the United States.

In 1992, the National Geologic Mapping Act was passed by Congress and signed by the president. Recently reauthorized, the national act supports federal, state, and educational mapping projects. And to ensure that the results of those efforts are easily accessible to all map users across the country, the law calls for the development of a National Geologic Map Database (NGMDB).

Congress placed the database under the management of the USGS. But from the beginning, the Survey and the AASG have been strongly committed to close cooperation on this project. The Digital Geologic Mapping Committee of AASG was formed to participate in developing the NGMDB.

The database, which covers themes of geology, geophysics, geochemistry, geochronology, and paleontology, will provide rapid access to state and federal agency map holdings. Users will be able to locate both digital and paper maps through the search of metadata at a central site.

DATABASE DESIGN

The NGMDB is designed not as a conventional, highly structured database, but rather as a distributed system of map data servers at many remote locations (for example, a state geological survey), accessed through a central site on the World Wide Web. That site, located at "http://ngmdb.usgs.gov", will contain a variety of national-scale, earth-science databases; a catalog of metadata that describes all available paper and digital earth-science maps; and a mechanism for searching the metadata and accessing the remote sites, which may contain map data on-line or ordering information for analog map products. This arrangement - a distributed system of data servers accessed by centralized searches of metadata - is similar to that used in the Geospatial Data Clearinghouse, coordinated by the National Spatial Data Infrastructure Initiative (see "http://www.fgdc.gov").

The NGMDB should be able to serve a specialized audience interested in a wide variety of information services related to the availability and use of earth-science maps. At present, only paper geologic maps are available for many parts of the country. Because it is important that the NGMDB be as useful and comprehensive as possible - as soon as possible - the database will offer access to paper as well as digital maps.

Our design was partly influenced by emerging philosophies for managing data and partly dictated by necessity. A single group cannot readily manage all geologic maps because they are produced by state geological surveys, several USGS scientific programs, universities, professional societies, and other organizations.

To provide users with access to information, as required by the National Geologic Mapping Act, the geological survey of each state has become a partner in the project, participating in the design and implementation of the database. Nationwide coordination is a challenge because of the wide variability in computer capability, staffing, and experience among the state surveys and the various USGS scientific programs. But uniformity of the products will be a key element in ensuring the utility of the NGMDB.

STATUS OF THE PROJECT

In the June 1995 issue of Geotimes, the plan for creating the National Geologic Map Database was described. In the year that followed, work focused on two issues: (1) building a prototype web site and establishing the NGMDB catalog format, and (2) developing a network of talented and dedicated collaborators. Without the broad-based, mostly volunteer support of various agencies and individuals, this project would have little chance for success.

More recently, the database began to be built. Information about its progress can be obtained by checking "http:// ncgmp.usgs.gov/ngmdbproject".

The most fundamental aspect of the project is the comprehensive catalog of abbreviated metadata, or bibliographic listings, for all published paper and digital maps. It is intended to be the user's primary means for identifying and gaining access to geoscience maps. This catalog is now being compiled under the supervision of Nancy Blair, USGS Western Region chief librarian.

Blair and her staff have completed the cataloging of all USGS map series and are working to incorporate those listings into the database catalog. They are now cataloging maps in the survey's book publications and open-file series.

We have begun the process of including maps produced by state geological surveys and other organizations by identifying a contact person at each agency to work with USGS library staff. Over the next year or so, we anticipate that these maps will gradually be entered into the database catalog. The web site's search page includes a ~thermometer" graphic that tracks our progress in building an up-to-date catalog of all maps.

It is important for all in the geoscience community to understand that the NGMDB catalog responds to a congressional mandate and that it is the primary catalog of geologic maps for the nation. We are concerned that the expenditure of tax dollars to build this catalog not be duplicated by other organizations at public expense. Other databases identifying and cataloging geologic maps and attendant metadata should reference the national database and dovetail with it.

A significant effort this past year focused on developing other useful features - including a National Paleontologic Database, a lexicon of geologic names (both led by Bruce Wardlaw, USGS), and a database of current geologic mapping activities (led by John Sutter, USGS). Designed to support users of earth-science maps, these features will also be searchable through the database web site.

CREATING NATIONAL STANDARDS

Full implementation of the NGMDB, especially for the management and serving of digital map data, requires certain standards and common practices. Standards development, which was mandated by the mapping act to ensure map users some uniformity of product, is a primary focus of the database project.

For many years, the need for standards has been a difficult issue for earth scientists. Partly because geologists are funded by many separate agencies, and partly because of the gradual maturing of digital mapping methods and their applications to earth science, standards for creating, managing, and publishing digital map information have not been effectively addressed across the geologic community.

Because the database requires a strong foundation of standards for its implementation, it was imperative that we organize an effort to accomplish this work. At a meeting in St. Louis in August 1996, the AASG and USGS representatives of the database project formed six working groups to develop standards and address other technological issues.

1. Cartographic Standards

This is a standard set of geologic map symbols, colors, and patterns. In the past year, an existing draft USGS standard was reviewed and a plan for developing a generally accepted federal standard (using the Federal Geographic Data Committee [FGDC] standards-development process) was outlined. As part of the database project, the geologic map symbolization standard is now being developed by the USGS Publications Group's Western Region team. We expect to release a draft suitable for public review through the FGDC Geologic Data Subcommittee in early 1998.

2. A Standard Geologic Data Model

This model will describe the organization of geologic map and legend information in various computer files, structured according to relational and object-oriented database design. This standard is critical both for the geoscience agencies that produce maps and for those who will eventually use these products.

Standardized formats for geologic maps should help promote the utility of the information compiled by encouraging the development of software tools for creating, analyzing, displaying, and producing geologic maps. Standardization should also increase the public's familiarity with, and ability to use, geologic maps.

The working group, let by Gary Raines and Bruce Johnson (USGS) and Boyan Brodaric (Geological Survey of Canada), has written a first draft of the model for general review. This draft draws upon lengthy discussions with working group colleagues in the state geological surveys and elsewhere. After extensive discussion and revision, the draft data model will be submitted to the FGDC for formal public review and consideration as a federal standard.

Developing a standard data model is a formidable challenge - especially for the geosciences. This is a new concept to most geologists, and the working group welcomes a "spirited" discussion of its merits and shortcomings. To help other geoscientists evaluate the model, prototype software tools are being developed for use with certain popular mapping and database software packages.

3. Data Capture

To promote better understanding of methods for digital mapping within the geoscience community, this working group conducted a workshop on digital mapping techniques in Lawrence, Kan., in June, 1997. The workshop was attended by more than 70 technical experts from 30 state surveys, the USGS, and the Geological Survey of Canada, who welcomed the opportunity to discuss specialized topics with new-found colleagues. Given the rapid evolution of digital mapping techniques, workshops of this kind are extremely useful, and are planned as a yearly activity.

(Presentations from the June meeting were summarized in a proceedings volume (USGS Open-File Report 97-269). Copies are available from the authors of this article.)

4. Metadata

These are guidelines for writing FGDC-compliant metadata for geoscience maps. Through coordination with similar efforts sponsored by the USGS Geologic Division Information Council and the GIS Division of the Geological Association of Canada, this working group has assembled guidance and information on useful tools and software. The utility of this "package" is being evaluated by the state geological surveys; comments from the geoscience community are also welcome.

5. Data Information Exchange

These are guidelines for publication of digital maps. The public will be able to use digital maps more efficiently if geoscience agencies provide a common set of files in their digital map publications. Someone who obtains maps produced by several agencies could work with these products more easily if they contained, for example, a README file, FGDC-compliant metadata, a common-format graphics file for viewing the map, and map data in common interchange formats. Improved and more standardized procedures for peer review of digital maps would be helpful, as would guidelines for methods of serving map data on-line. Recommendations from this group are under development.

6. Spatial Accuracy

As a first task, this group was asked to prepare a general-interest publication to explain the nature of geologic mapping and reasons why the spatial accuracy of geologic lines may differ from the locational accuracy of other map themes (for example, pipelines). Given the ease of comparison of map themes provided by geographic information systems, this document should be a useful aid to the map user, and could be referenced within a map's metadata (specifically, within the "positional accuracy" section).

1998 AND BEYOND

The database project is now moving beyond a strictly developmental stage. As the project matures, we will focus on broadening and solidifying our base of partners, building collections of well-documented digital maps in standard formats, and developing more efficient and useful ways to deliver them to the public. We also plan to set up links through the web site to other map producers (especially for geochemical and geophysical information) and to evaluate emerging technologies for potential application to this effort.

Because the database is intended to address the public's needs, we invite you to contact us with your advice, questions, or concerns.

David R. Soller

U.S. Geological Survey, 908 National Center, Reston, Va. 20192. E-mail: "drsoller@usgs.gov". WWW: "http://ncgmp.usgs.gov/drs.html".
A research geologist, Soller serves as program deputy for the National Cooperative Geologic Mapping Program. His responsibilities include coordinating the design and implementation of the National Geologic Map Database and research and applications on new uses of earth-science information for societal decision-making.